An Extended Pseudo Trunk (abbreviated as XPT in English) system is a distributed trunking system without a control center. One XPT system may be composed of a plurality of stations, each station has a plurality of repeaters providing a shared channel, and the plurality of repeaters include a fixed master repeater and a plurality of slave repeaters. The XPT system can maximize the system capacity without increasing additional cost, effectively utilize the existing channel resources, and can fully meet the demands of mid-and-low-end trunking customers. The XPT system does not need a designated control channel. This solution can meet US FB6 frequency specifications, and its frequency allocation can be shared with other systems, for example, the same frequency can be allocated to different users. Therefore, the XPT system is widely applied due to low cost and high channel resource utilization thereof.
In the related art, there is a situation that people in the same call always occupy the channel, resulting in a receiving terminal being unable to interrupt a call of a transmitting terminal to initiate a callback. Moreover, in the case that all the channel resources are occupied, users with high priority cannot interrupt the channel resources to initiate a call if they want to initiate a general call or an emergency call. Therefore, there is a need for a method that can interrupt the call of the transmitting terminal to meet the demands of the users.
In the existing centralized trunking system, each terminal is managed by a designated control channel and a specialized control center. At ordinary times, the control channel remains in a long transmission state, and all the terminals are waiting on the control channel. When all the channels in the system are occupied, the control center can release the channel resources by issuing a Reverse Channel (RC) instruction to a designated terminal. However, this method requires the designated control center and the designated control channel to manage the terminals. The issuing the RC instruction to release the channel resources by the control center when the channel resources are fully occupied is not suitable for a receiving terminal of a distributed trunking system without a control center to interrupt a call of a transmitting terminal. Therefore, in the distributed trunking system without a control center, how to use the current system resources to interrupt the call of the transmitting terminal so as to reduce the waste of the channel resources becomes a matter of concern.